Worldwide there are about 1500-2000 brown seaweed species.
Brown algae belong to a very large group, the Heterokontophyta, a eukaryotic group of organisms distinguished most prominently by having chloroplasts surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment fucoxanthin, which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with differentiated tissues, but they reproduce by means of flagellate spores, which closely resemble other heterokont cells. Genetic studies show their closest relatives to be the yellow-green algae.
The plants are filamentous, macroscopic or microscopic some polyiphonous. Some form crusts, cushions or are hollow and others grow to form large leathery fronds. The cells of most browns are connected by pores. They bear a unilocular (one holed) sporangium.
Phaeophyta evolved from the phaeothamniophyceae between 150 & 200 million years ago. Claims that earlier (Ediacaran) fossils are brown algae have since been dismissed.
The linages of brown algae diverged in the following order, from oldest to youngest: Dictyotales; Sphacelariales; Cutleriales; Desmerestales; Ectocarpales; Laminarales; Fucales.
Their occurrence as fossils is rare due to their generally soft-bodied habit, and scientists continue to debate the identification of some finds. Other algae groups, such as the red algae and green algae have a number of calcareous members, which are more likely to leave evidence in the fossil record than the soft bodies of the brown algae. Miocene fossils of a soft-bodied brown macro algae, Julescrania, have been found well-preserved in Monterey Formation diatomites, but few other certain fossils, particularly of older specimens are known in the fossil record.
Brown algae growing in brackish waters are almost solely asexual.
They have Cellulose walls with alginic acid; fucoidin also important in amorphous section of cell walls. A few species (of Padina) calcify with aragonite needles.
Research Findings from Virginia Polytechnic Institute and State University Update Understanding of Aquaculture
Apr 02, 2013; By a News Reporter-Staff News Editor at Life Science Weekly -- Investigators publish new report on Aquaculture. According to news...